• Journal of the Korean Society of Propulsion Engineers
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• v.14 no.5
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• pp.92-100
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• 2010

Combustion stability rating tests of 75-tonf-class thrust chamber for technology demonstration were carried out at a low pressure. Two kinds of mixing heads were used in this study. One of them has injectors of 631 and the other has injectors of 721. Mixing head with injectors of 631 showed a self-oscillation instability at the chamber pressure of 30 bar. Mixing head with injectors of 721 showed that a high frequency combustion stability was maintained under the same pressure and the same mass flow rate. But mixing head with injectors of 721 generated a self-oscillation instability at the chamber pressure of 20 bar and it was found that stability boundary region was changed due to the configuration of a mixing head from these results.

• Journal of the Korean Society of Propulsion Engineers
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• v.22 no.4
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• pp.85-90
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• 2018

The objective of this paper is to observe effects of ignition position and time on ignition transition. A gaseous oxygen and liquid kerosene mixture is used as propellant with a shear-coaxial injector. In order to study the ignition delay time and combustion instability intensity, the pressure transducer was used. Sequences, excepting igniter operation time, were fixed to compare the ignition time only. Initial pressure peak and ignition delay time increased as the ignition time was delayed. Additionally, an unstable flame development zone was detected when the igniter was away from the injector.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.7
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• pp.695-702
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• 2008

Flow instability in the rocket turbo pump systems can be caused by various elements such as valve, orifice and venturi and etc. The formation of cavitation specially in the propellant feeding system can trigger the mass flow and pressure oscillation due to cyclic formation and depletion of cavitations. If the cryogenic propellant are used, which is very sensitive to temperature variation, the change of propellant properties due to thermodynamic effect should be accounted for in the flow analysis. This study focuses on the formation of cryogenic cavitation adopting MUSHY IDM model suggested by Shyy and coworkers. Also, the flow instability is investigated with developed numerical code in the downstream of orifice flow. To this end, three different orifices are selected and investigated by the numerical calculation.

• Journal of the Korean Society of Propulsion Engineers
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• v.22 no.3
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• pp.72-80
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• 2018

Combustion instabilities are caused by the feedback relationship between heat release perturbations and acoustic pressure oscillations in the combustor. Studies on the combustion instability in an annular combustor have recently received great attention due to the enhanced NOx requirement in aero-engines. In this study, a thermoacoustic network model was developed in order to calculate the acoustic characteristics for various modes in the annular combustor. The network model is combined with flame transfer function(FTF) in order to calculate the stability of the combustor. Numerical results are compared with measurement data.

• Journal of the Korean Society of Propulsion Engineers
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• v.24 no.1
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• pp.24-33
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• 2020

In this study, model combustion tests were conducted to investigate the combustion instability characteristics of swirl coaxial injectors for a liquid rocket engine. To examine the effects of the combustion chamber resonant frequency and the injector mixing conditions, pressure fluctuations in the combustion chamber were measured by changing the combustion chamber length, injector recess length, and propellant mixture ratio. From the test results, the variation in the pressure fluctuations for each experimental condition was confirmed and the combustion stability was evaluated by stability mapping. It was found that the longitudinal mode and Kelvin-Helmholtz instabilities occurred due to the change in the combustion chamber and recess lengths.

• Journal of the Korean Society of Propulsion Engineers
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• v.14 no.2
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• pp.19-28
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• 2010

Generally, combustion instability is generated by the mutual coupling between the heat release and the acoustic pressure in the combustor. On the occasion, the acoustic pressure generates the oscillation of the mass flow rate of propellant injected from injector, and this oscillation again affects combustion in the combustor. So, the dynamic characteristics of the injector have been studied to control combustion instability using injector itself in Russia from 1970's. In order to study injector dynamics, a mechanical pulsator for forced pressure pulsation is produced and the method to quantify the mass flow rate of the propellant that is oscillating at the exit of the injector is developed. With the pulsator and the method, pulsating values of the mass flow rate, pressure, liquid film thickness, and axial velocity generated at the exit of the simplex swirl injector are measured in real time. And phase-amplitude characteristics of each parameter are analyzed using these pulsating values acquired at the exit of the simplex swirl injector.

• Proceedings of the Korean Nuclear Society Conference
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• 1998.05b
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• pp.851-856
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• 1998

국내에서 상업운전중인 월성 원자로는 캐나다에서 개발한 CANDU형 원자로로 핵연료를 지지하는 핵연료 압력관이 사용되며, 핵연료 압력관은 원자로의 1차기기로 건전성확보가 매우 중요하다. 가동중 검사시 압력관에서 결함이 검출되면, 지속적인 사용을 위해서 결함의 건전성을 확보하여야하나, 그 평가절차가 매우 복잡하다. 본 연구에서는 핵연료 압력관 평가를 보다 신속하고 효율적으로 수행하기 위한 건전성 평가시스템을 개발하였다. 개발된 평가시스템은 예리한 결함 및 둔한 함에 대한 평가를 수행할 수 있으며, 피로균열평가, 지체수소균열평가, 불안정파괴평가, 파단전누설평가, 소성붕괴평가모듈을 수록하고 있다. 또한 개발된 시스템을 검증하기 위하여 캐나다 ECL에서 제시한 평가결과와 비교함으로서 본 시스템의 효용성을 검증하였다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2001.04a
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• pp.17-20
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• 2001

Combustion characteristics of KSR-III liquid rocket engine are investigated numerically in the standpoints of engine performance and acoustic instability. In the present calculation, engine performance for design and off-design conditions is estimated effectively with reasonable error. Numerical results of acoustic instability show that engine operation for the design condition has sufficient stability margin, but for a certain off-design condition, acoustic instability can be triggered by artificial pressure perturbation. The present results are in a good agreement with the available experimental results and can be adopted for the prediction of engine performance and stability, depending on the specific operating condition.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.12
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• pp.1021-1027
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• 2018

Experimental studies have been conducted to verify that the positive coupling between pressure oscillation (p') and combustion oscillation (q') of high frequency range is a prerequisite for the initiation of low frequency instability in hybrid rocket combustion. The post-chamber length and combustion equivalence ratio were selected as critical parameters to control the phase difference between p' and q', and p' amplitude in relation to the suppression of LFI. In the results, even if the post-chamber length increases, the phase difference between p' and q' maintains below pi/2, which is a necessary condition for the LFI development, but the amplification of RI (Rayleigh index) was substantially decreased leading to a stable combustion. In addition, results confirmed that combustion stability is achieved by changing the momentary equivalence ratio and/or by suppressing the positive coupling status of p' and q'. Thus, the periodic amplification of RI was identified as the middle path of the mechanism of occurrence of LFI.

• Proceedings of the Korean Society of Computer Information Conference
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• 2019.01a
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• pp.291-292
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• 2019

본 논문에서는 자세 교정에 도움을 줄 수 있는 압력센서 기반의 스마트 방석 개발 사례를 소개한다. 스마트 방석은 스마트폰과 블루투스로 연결되며 스마트폰 앱은 사용자의 자세 정보를 분석한 후 자세가 불안정한 징후가 판단되면 알림을 통해 바람직한 자세를 취할 수 있도록 안내한다. 본 시제품 개발에서는 압력센서의 값을 분석한 후 단순한 형태의 자세 추정 방식을 채택하였지만 향후 다양한 실험 및 딥러닝 응용을 통해 정확한 자세 추정을 위한 알고리즘을 개발할 계획이며 알림에 의한 수동적 자세 교정이 아닌 기구 설계, 모터 제어 등을 통해 능동적인 자세 교정을 지원하는 스마트 방석을 개발할 계획이다.